1. Field
The present specification generally relates to separating strengthened glass substrate sheets and, more particularly, to forming at least one groove within a glass substrate sheet prior to a strengthening process in order to separate glass articles from strengthened glass substrate sheets by self-propagation of a through crack along the groove.
2. Technical Background
Thin glass articles have a variety of applications in consumer electronic devices. For example, such glass articles may be used as cover sheets and/or touch screens for LCD and LED displays incorporated in mobile telephones, GPS devices, display devices such as televisions and computer monitors, and various other electronic devices. As the use of glass articles in various devices continues to expand, the geometric complexity of the glass articles also increases. For example, certain applications may require that the glass articles be formed with complex shapes, such as curved peripheries and/or through-features, thus requiring additional machining operations to achieve the desired geometry.
The glass articles may be formed by separating a glass substrate sheet into a plurality of discrete glass articles. In addition, the glass substrate sheet may be formed from damage resistant glass, such as ion-exchanged glass or similarly strengthened glass. For example, the ion-exchange process creates a compressive stress at the surfaces of the glass substrate. These compressive stresses extend from the surfaces of the glass substrate to a certain depth, referred to as the depth of layer. The surface compressive stresses are balanced by a central layer or region of tensile stresses (referred to as central tension) such that the net stress in the glass substrate is zero. The formation of compressive stresses at the surface of the glass substrate makes the glass strong and resistant to mechanical damage and, as such, mitigates catastrophic failure of the glass substrate by preventing flaws introduced on the surface from propagating through the depth of layer.
When glass articles are ion exchanged after separation, both the surface and edges of the article are strengthened and damage resistant. However, there is the case where it is desirable to separate the glass sheet into individual articles after the ion exchange process. In this case, the newly formed edges have not been ion exchanged and are susceptible to damage from mechanical contact. More specifically, separating the glass substrate after ion-exchange processing leaves the central tension layer exposed at the edges of the separated glass article, thereby leaving the edge susceptible to damage that may lead to catastrophic failure of the article.